1. Technical Field
The present invention relates to an image-forming apparatus that forms an image on a sheet.
2. Background Art
An image-forming apparatus adopting an electrophotographic system such as a printer, a copier, a facsimile and the like has been widely used in the past. Such an image-forming apparatus has formed toner images of respective colors of yellow, cyan, magenta and black on photoreceptors corresponding to each color and then, it has transferred these toner images on an intermediate transfer belt with overlapping them in order. The image-forming apparatus has transferred the transferred toner images on a sheet being transported at once to form a color image.
In the image-forming apparatus, it has been desirable to keep a toner adhesion amount stable in order to maintain stable an image density of the toner image on the sheet. For that purpose, in the image-forming apparatus, a sensor has detected a toner adhesion amount of a patch, which is a toner image for a test and is formed on an image carrier such as the intermediate transfer belt. Based on this detection result thereof, the image-forming apparatus has controlled the toner adhesion amount of the image by adjusting any image-forming conditions such as charged voltages and developing bias voltages.
The image-forming apparatus may generate any failure in the image density by changing, for example, any image-forming conditions in a transfer portion, any fixing conditions in a fixing portion and/or the like. Accordingly, in recent years, an image-forming apparatus has been developed in which an image density sensor is provided at a downstream side of the fixing portion and the toner adhesion amount is controlled on the basis of an output of this image density sensor to attain stability in the image density.
Each of Japanese patent application publications Nos. 2007-199466 and 2006-171104 discloses the image-forming apparatus which has any faculty to attain stability in the image density. For example, Japanese patent application publication No. 2007-199466 discloses the image-forming apparatus which can keep an output image density stable by controlling a target value of the toner adhesion amount according to a fixing temperature, a fixing speed and species of sheet. On the other hand, Japanese patent application publication No. 2006-171104 discloses the image-forming apparatus which adjusts the image density by the developing bias and then, adjusts glossiness by the fixing temperature with adding image density value thereto.